This invention relates to radial ply pneumatic vehicle tires and more particularly to such tires having reinforcements in the regions of the beads and the lower sidewalls.
The expression "radial tires" and "radial ply tires" as commonly used in the pneumatic tire art may be said to include the various tire constructions having a carcass or body comprising one or more reinforcement plies of rubberized tire cords extending from bead to bead wherein the cords in each ply are substantially radial in orientation, i.e., the cords are oriented substantially normal to the beads and to the crown center-line of the tire. In a mono-ply tire the carcass or body cords normally have 90.degree. bias angle, i.e., in the unshaped carcass they extend perpendicular to the planes of the beads. In a two-ply radial tire, the cords in each body ply are usually oriented at oppositely disposed small angles of up to 10.degree. with respect to the perpendicular to the bead planes, in which case the respective body plies are said to have oppositely disposed bias angles of 80.degree. or greater (but less than 90.degree. ). In four ply or heavier radial ply tire constructions similar opposed orientation of the cords in successive body plies is usually employed. All of these body or carcass constructions are contemplated within the scope and meaning of the expressions "radial" and "substantially radial" as used herein.
It is known that in radial ply carcass tires the beads and lower sidewall areas are the most delicate regions of the tire structure due to the considerable stresses to which they are subjected. This is due to the fact that the sidewalls of radial ply tires deform substantially in a vertical direction under load. The consequent repeated flexing of the lower tire sidewalls combined with the stresses imposed thereon result in premature deterioration of the lower sidewall regions and the beads. The phrase "lower sidewall region" is used here to mean that region of the tire which extends from the tire bead up to that point on the tire at which the width of the tire cross-section is a maximum, i.e., the mid-circumferential plane of the tire. The aforementioned deterioration of the tire is due both to, as aforestated, the detachment and rupture of the carcass plies in the lower sidewall region of the tire and due to friction between that region of the tire and the flange of the wheel rim on which the tire is mounted.
It is known in the radial ply tire art that, to minimize the aforenoted disadvantages, it is desirable to stiffen the bead regions of the tire. To this end the beads have been constructed to include, in addition to the metal wire bead ring, and the carcass plies which are turned up about the ring, reinforcements of various kinds such as, for example, hard rubber fillers, which are generally triangular in cross-sectional configuration and which extend radially outward of the bead ring and by flippers which are made of rubberized tire cord fabric, have a tear drop shaped cross-sectional configuration and envelop the bead ring and bead filler. It is further known, in an attempt to overcome the aforenoted disadvantages, to further stiffen the bead regions of a radial ply tire by including one or more strips of radially extending rubberized cord fabric in the bead regions of the tires, as illustrated, for example, in U.S. Pat. No. 3,557,860.
The foregoing constructions are, however, not completely satisfactory in that they do not provide sufficient bonding between the tire bead unit and the carcass, they do not provide sufficient reinforcement for the lower sidewall region of the tire and, as a consequence of the foregoing, they do not provide a tire having the desired degree of stability.